By chance, the applicant has produced a truncated mutant of Bax, which turned out to be a potent suppressor of neuronal apoptosis. Much of his application will focus on this finding. He will begin by investigating the mechanism by which sympathetic neurons mature to a non-NGF dependent state; he proposes 3 hypotheses to test here: (a) loss of dependence is due to an alteration in pattern of expression of members of the BCL-2 family; (b) a protein is expressed that sequesters BAX in cytoplasm, thus preventing its translocation to the mitochondria; or (c) there is an age-dependent post-translational modification of BAX. The second specific aim is to extend structure-function analysis of truncation mutants of Bax as suppressors of neuronal apoptosis. He will also determine if truncation mutants of other pro-apoptotic members of the BCL-2 family are anti-apoptotic. His third specific aim is see if truncated BAX also protects other cell types, including macroglia, fibroblasts, and lymphocytes, against apoptosis. Specific aim 4 will test whether truncated Bax blocks translocation of BAX to the mitochondria, or the loss of cytochrome c from the mitochondria. Finally, with an experienced collaborator, the investigator will generate tBAX transgenics.